1. Field of the Invention
The present invention relates to a halftone display method and display apparatus for displaying halftone gray scale images by using an intraframe or intrafield time-division method, and more particularly, to a halftone display method and display apparatus which can reduce halftone disturbances occurring in moving image portions displayed on a gas discharge display panel and can prevent the occurrence of moving-image false contours (false color contours) in such images.
2. Description of the Related Art
In recent years, with increasing display screen size, the need for thin display apparatuses has been increasing, and various types of thin display apparatus have been commercially implemented. Examples include matrix display panels that display images by directly using digital signals, such as plasma displays and other gas discharge display panels, the Digital Micromirror Device (DMD), EL display devices, fluorescent display tubes, liquid crystal display devices, etc.
Among such thin display devices, gas discharge display panels are considered to be the most promising candidate for large-area, direct-view HDTV (high-definition television) display devices, since they can be easily made large in area because of their simple fabrication process, can provide good display quality because of their self-luminescent characteristics, and can have high response speed. Such display devices, however, have the problem that disturbances occur in halftone areas of moving images, impairing the display quality.
To address this problem, it has been proposed to reduce false contours by superimposing positive or negative equalizing pulses on the source signal. However, as the image moving speed increases, the image disturbances become visible.
In the prior art, if the gray-scale level change is smooth, that is, if the pitch (number of pixels) over which the same luminance block having the largest weight changes is greater than the image moving distance per frame, then correct motion compensation is possible since the number of pixels to which equalizing pulses are applied is equal to the moving speed. However, in the case of a fine pattern, it is difficult to detect the correct speed, and the moving speed may be detected, for example, as being one pixel per frame, resulting in an inability to reduce the disturbances sufficiently. Namely, in the prior art, a halftone displaying technique has been proposed that does not cause disturbances in halftone display, but it is desired to further improve the display quality.
Prior art and the problems thereof will be explained later with reference to accompanying drawings.
An object of the present invention is to provide a halftone display method and display apparatus which, when using an activation sequence having redundancy that enables one gray-scale level to be displayed by any one of a plurality of combinations of subframes (luminance blocks), can reduce the occurrence of moving-image false contours (false color contours) in video by actively utilizing the redundancy.
According to the present invention, there is provided a halftone display method which predefines a plurality of luminance blocks in each frame or field to display an image, and which is capable of displaying one gray-scale level by any one of a plurality of combinations of the luminance blocks, wherein when determining luminance blocks for use to display the gray scale of an arbitrary first pixel, the luminance blocks to be used for the first pixel are selected in accordance with a predetermined rule, based on how the luminance blocks are used for a second pixel located in close proximity to the first pixel.
Further, according to the present invention, there is also provided a display apparatus which predefines a plurality of luminance blocks in each frame or field to display an image, and which is capable of displaying one gray-scale level by any one of a plurality of combinations of the luminance blocks, comprising an image display; a driving unit for driving the image display; a control unit for controlling the driving unit; and a luminance block selection and luminance adjusting luminance block insertion unit for selecting luminance blocks, and for inserting a luminance adjusting luminance block into a source signal, and wherein when determining luminance blocks for use to display gray scale of an arbitrary first pixel, the luminance block selection and luminance adjusting luminance block insertion unit selects the luminance blocks to be used for the first pixel in accordance with a predetermined rule, based on how the luminance blocks are used for a second pixel located in close proximity to the first pixel.
The second pixel may be a pixel that is producing the same color as the first pixel, and that is located closest to the first pixel horizontally or vertically. If the second pixel does not exist on a display screen, the second pixel may be assumed to be displaying an arbitrarily set gray-scale level.
The plurality of luminance blocks predefined in each frame or field may be provided with redundancy such that more than one luminance block is assigned the largest luminance weight. How the luminance blocks with the largest luminance weight are to be used for said first pixel may be determined based on how the luminance blocks with the largest luminance weight are used for said second pixel. How many luminance blocks with the largest luminance weight are to be used for the first pixel may be determined based on how many luminance blocks with the largest luminance weight are used for the second pixel.
All gray-scale levels may be classified into groups according to the number of luminance blocks with the largest luminance weight that are allowed to be used; the first and the second pixel may be assigned group numbers from the classified groups according to the gray-scale levels that the first and the second pixel display; and the group numbers assigned to the first and the second pixel may be compared with each other and, in accordance with the result of which, one of the plurality of combinations of the luminance blocks is selected to display the gray-scale level of the first pixel. The gray-scale level to be displayed by each pixel may be expressed by one of two descriptions, the first description using a smaller number of luminance blocks with the largest luminance weight than the second description; and the number of luminance blocks with the largest luminance weight to be used for the first pixel may be determined by comparing the group number, denoted as GA, of the first pixel with the group number, denoted as GB, of the second pixel, and by selecting one of the two descriptions in such a manner that when GB less than GA, the first description may be selected; when GB=GA, the same description as used for the second pixel may be used; and when GB less than GA, the second description may be selected.
How the luminance blocks with the largest luminance weight to be used for the first pixel are selected from among the luminance blocks with the largest luminance weight may be determined according to how the luminance blocks with the largest luminance weight are selected and used for the second pixel. When there occurs a state change between successive frames or fields in any one of the luminance blocks with the largest luminance weight in the first pixel, the number of linearly contiguous pixels on a display screen that exhibit the same change as the change in the one of the luminance blocks with the largest luminance weight in the first pixel may be detected; a predetermined luminance adjusting luminance block may be selected based on the detected number of contiguous pixels and on the change in the one of the luminance blocks with the largest luminance weight in the first pixel; and the selected luminance adjusting luminance block may be applied to a source signal of each of the contiguous pixels.
The selected luminance adjusting luminance block may be applied not only to the source signal of each of the detected contiguous pixels but also to the source signal of an additional pixel located on the opposite side of the contiguous pixels from the second pixel. The detection of a state change between successive frames or fields in the luminance blocks with the largest luminance weight may be performed in sequence, starting with the luminance block located on the smaller luminance weight side of the luminance blocks with the largest luminance weight.
When there occurs a state change between successive frames or fields in any one of the luminance blocks with the largest luminance weight in the first pixel, the number of linearly contiguous pixels on a display screen that exhibit the same change as the change in the one of the luminance blocks with the largest luminance weight in the first pixel may be detected in a horizontal and a vertical direction; a predetermined luminance adjusting luminance block may be selected based on the detected number of horizontally or vertically contiguous pixels, whichever is smaller, and on the change in the one of the luminance blocks with the largest luminance weight in the first pixel; and the selected luminance adjusting luminance block may be applied to a source signal of each of the contiguous pixels.
The selected luminance adjusting luminance block may be applied not only to the source signal of each of the horizontally or vertically detected contiguous pixels, whichever are smaller in number, but also to the source signal of an additional pixel located on the opposite side of the contiguous pixels from the second pixel. The plurality of luminance blocks may be 10 in number, and the luminance weights of the luminance blocks may be set to provide gray-scale levels 1, 2, 4, 8, 16, 32, 48, 48, 48, and 48, respectively.
According to the present invention, there is provided a halftone display method which predefines a plurality of luminance blocks in each frame or field to display an image, and which is capable of displaying one gray-scale level by any one of a plurality of combinations of the luminance blocks, wherein when determining luminance blocks for use to display a gray scale of an arbitrary first pixel, the luminance blocks to be used for the first pixel are selected in accordance with a predetermined procedure based on the state of the luminance blocks in at least two reference pixels around the first pixel.
Further, according to the present invention, there is also provided a display apparatus which predefines a plurality of luminance blocks in each frame or field to display an image, and which is capable of displaying one gray-scale level by any one of a plurality of combinations of the luminance blocks, comprising an image display; a driving unit for driving the image display; a control unit for controlling the driving unit; and a luminance block selection and luminance adjusting luminance block insertion unit for selecting luminance blocks, and of inserting a luminance adjusting luminance block into a source signal, and wherein, when determining luminance blocks for use to display a gray scale of an arbitrary first pixel, the luminance blocks to be used for the first pixel are selected in accordance with a predetermined procedure based on the state of the luminance blocks in at least two reference pixels around the first pixel.
The reference pixels may be located directly adjacent to the first pixel. The reference pixels may be located directly adjacent to or in proximity to the first pixel through other pixels.
The luminance blocks to be used for the first pixel may be selected based on the state of the luminance blocks exceeding a majority of the reference pixels. The reference pixels may be an even number, and in the case where the reference pixels of different luminance blocks are equally divided in number, the luminance blocks to be used for the first pixel may be maintained without changing.
The reference pixels may be weighted according to the relative position thereof with the first pixel, respectively, and the luminance blocks to be used for the first pixel may be selected based on the state of the luminance blocks of the weighted reference pixels. In the case where the weighted reference pixels of different luminance blocks are the same, the luminance blocks to be used for the first pixel may be maintained without being changed.
The display apparatus may further comprise a lighting pattern setting unit for setting the whole display screen in a predetermined lighting pattern. The lighting pattern setting unit may set each pixel of the whole display screen in a luminance state using a maximum number of luminance blocks having the largest luminance weight.